Millions of people have suffered from breast cancer and other types of cancer. It is estimated that in the United States, breast cancer mortality is second only to that of lung cancer. Because of its role in early tumor detection, mammography has become the most commonly used tool for breast cancer screening, diagnosis and evaluation in the United States. A mammogram is an x-ray image of inner breast tissue that is used to visualize normal and abnormal structures within the breasts. A common purpose of breast imaging is to identify and assess potential pathologies or other abnormalities, which most frequently appear as likely micro-calcifications, tumor masses and architectural distortions. Mammograms provide early cancer detection because they can often show breast lumps and/or calcifications before they are manually palpable.
While screening mammography is recognized as the most effective method for early detection of breast cancer, the modality has limitations. One problem with known mammogram systems and methods lies in their low specificity. More particularly, it is often difficult to determine whether a detected abnormality is associated with a cancerous or benign lesion. This difficulty arises from the fact that a mammogram is two dimensional (2D) representations of a three dimensional (3D) structure, and overlapping structures in the compressed breast may confound diagnosis. These difficulties are further complicated in view of different breast compositions.
For example, breast composition, including breast x-ray density and texture, can vary from one patient to another, from one breast to another of the same patient and even within a single breast. Some breasts are composed mainly of fatty tissue and are known as “fatty breasts,” while others have a high percentage of fibro glandular tissue and are known as “dense breasts.” Most breast compositions are somewhere in between.
Efforts to improve the sensitivity and specificity of breast x-rays have included the development of breast tomosynthesis systems. Breast tomosynthesis is a 3D imaging technology that involves acquiring images of a stationary compressed breast at multiple angles during a short scan. The individual images are then reconstructed into a series of thin, high-resolution slices that can be displayed individually or in a dynamic cine mode. Reconstructed tomosynthesis slices reduce or eliminate the problems caused by tissue overlap and structure noise in single slice 2D mammography imaging. Digital breast tomosynthesis also offers the possibility of reduced breast compression, improved diagnostic and screening accuracy, fewer recalls, and 3D lesion localization. Examples of breast tomosynthesis systems are described in U.S. Pat. Nos. 7,245,694 and 7,123,684, commonly owned by the Assignee of this application, the contents of which are incorporated herein by reference.
One goal of any x-ray imaging system is to obtain the highest quality image while minimizing the patient dose. Tomosynthesis acquisition systems balance the two goals by identifying a scanning protocol that obtains sufficient data to generate a quality reconstruction. The scanning protocol defines the number of images obtain during a scan, the angular range of the scan and the duration of the exposures. For example, a current tomosynthesis product is designed to perform a sweep angle of 15 degrees in about 5 seconds, during which 15 projections are acquired. The scanning protocol is generally fixed and used on all breast sizes and compositions.
While certain 2-D mammography systems have been introduced that vary, for example, the exposure time based on a measured thickness of the breast (determined by a distance between compression paddles), in general breast imaging systems lack the capability of customizing image acquisition parameters according to one or more of the preferred embodiments described herein.